The present invention relates to apparatus for and method of producing a resin-encapsulated semiconductor device by encapsulating, with an encapsulating resin material, a lead frame or a substrate which holds a semiconductor chip.
To accommodate the miniaturization of electronic devices, it is increasingly required to mount semiconductor elements with high density. To meet such demand, semiconductor devices are further miniaturized and thinner.
With reference to attached drawings, the following description will discuss a conventional resin-encapsulated semiconductor device producing method of hermetically encapsulating a semiconductor chip with a mold resin material.
FIG. 10(a) to FIG. 10(a) and FIG. 11(a) to FIG. 11(c) illustrate a resin-encapsulated semiconductor device producing method of prior art. FIG. 10(a) to FIG. 10(c) show a semiconductor device in section at a die bonding step and a wire bonding step, and FIG. 11(a) to FIG. 11(c) show a semiconductor device in section at a resin encapsulating step and an external electrode forming step.
As shown in FIG. 10(a), there is prepared a lead frame 101 having an inner lead portion 101a and a die pad portion 101b. The die pad portion 101b is held by a hanging lead (not shown). The hanging lead has a depressed portion which sets the die pad portion 101b at a position higher than the top of the inner lead portion 101a.
At a die bonding step in FIG. 10(b), the die pad portion 101b of the lead frame 101 is bonded to a semiconductor chip 102 with adhesives or the like.
At a wire bonding step in FIG. 10(a), the inner lead portion 101a of the lead frame 101 is electrically connected to the semiconductor chip 102 bonded to the die pad portion 101b with metallic fine lines 103.
Such a lead frame 101 and semiconductor chips 102 wire-bonded thereto are held by an encapsulating mold unit 131 of a semiconductor device producing apparatus as shown in FIG. 11(a).
The encapsulating mold unit 131 of the producing apparatus comprises an upper mold 131a and a lower mold 131b. The upper mold 131a is arranged to determine the shape of the resin material at the bottom sides of the die pad portions 101b of the lead frame 101. The lower mold 131b has a plurality of cavities 131a for determining the shape of the resin material at the top sides of the semiconductor chips 102 in the lead frame 101.
An ejector plate unit 132 and a plurality of ejector pins 133 are disposed at the encapsulating mold unit 131. The ejector plate unit 132 comprises an upper ejector plate 132a and a lower ejector plate 132b, these plates being disposed under the lower mold 131b. The ejector pins 133 vertically pass through the lower mold 131b and are vertically movable. In the ejector pins 133, the one ends project from the bottoms of the cavities 131c, the other ends are secured to the upper ejector plate 132a, and the lateral sides come in contact with the lower mold 131b. Disposed at the lower ejector plate 132b is an ejector rod 134 which is connected to the bottom of the lower ejector plate 132b for moving the ejector plate unit 132 and the ejector pins 133 in the opening direction of the cavities 131c.
A runner 131d is disposed between adjacent cavities 131c and communicates with gates 131e each of which is disposed, as a resin material inlet port, for each of the cavities 131c.
A molten resin material is injected into the cavities 131c through the runner 131d and the gates 131e to encapsulate, into a unitary structure, the inner lead portion 101a and the die pad portions 101b of the lead frame 101, and the semiconductor chips 102. Then, the encapsulated structure is subjected to a predetermined heating treatment to harden the resin material.
Then, the upper mold 131a is separated from the lower mold 131b, and the ejector rod 134 is then upwardly moved to push out a molded article made of hardened resin material through both the ejector plate unit 132 connected to the ejector rod 134, and the ejector pins 133.
Generally, one to about five ejector pins 133 are disposed for one molded article. The number and positions of the ejector pins 133 are determined according to the sizes of a molded article particularly to minimize the stress applied to the semiconductor chips 102 inside of the molded article at the time when the molded article is pushed out.
As shown in FIG. 11(b), an encapsulated resin body 104 is obtained by cutting the molded article at the runner 131d and the gates 131e. For simplification sake, only one encapsulated resin body 104 is shown in FIG. 11(b). However, since the lead frame 101 is rectangular, a plurality of encapsulated resin bodies 104 can be obtained.
Then, as shown in FIG. 11(c), there are cut and removed those portions of the inner lead portion 101a of the lead frame 101 which project from the encapsulated resin body 104. Thus, the end surface of the inner lead portion 101a is substantially flush with the lateral sides of the encapsulated resin body 104.
However, such conventional apparatus for and method of producing a resin-encapsulated semiconductor device is disadvantageous in the following points.
When the encapsulated resin body 104 thickness determined by the depth A of the cavities 131c shown in FIG. 11(a), is to be changed according to the shape of the encapsulated resin body 104 as in QFP (quad flat package) or TQFP (thin quad flat package), it is required to newly produce an encapsulating mold unit 131 corresponding to the changed thickness of the encapsulated resin body 104. The production of a new encapsulating mold unit 131 takes much time and cost. This constitutes a first problem that when the encapsulated resin body 104 of a resin-encapsulated semiconductor device is changed in thickness, a large number of man-hours is required for mass production of such encapsulated resin body 104 changed in thickness. Further, when there are prepared a variety of encapsulating mold units 131 corresponding to different thicknesses of encapsulated resin bodies 104, this not only takes a large number of man-hours for maintaining and managing such encapsulating mold units 131, but also requires a space for storing such encapsulating mold units 131.
Moreover, a resin-encapsulated molded article is pushed out by the ejector pins 133 disposed at the encapsulating mold unit 131. As mentioned earlier, one to five ejector pins 133 are used for one molded article. Accordingly, at the time of pushing-out, stress is concentrated on those portions of the molded article which come in contact with the ejector pins 133. This constitutes a second problem. In the worst case, a semiconductor element of a semiconductor chip 102 inside of a molded article might be broken due to the stress at the time when the molded article is pushed out. Further, the ejector pins 133 of prior art project to a height of about 0.1 mm to about 0.2 mm from the bottom of the cavities 131c. Accordingly, at the time of resin-encapsulation, those portions of the ejector pins 133 projecting into the cavities 131c prevent the injected resin material from freely flowing, thus producing a flow resistance. This involves the likelihood that the resin material does not flow uniformly. Also, after molding, the traces of the ejector pins are left on the molded article. This restricts that surface zone of the encapsulated resin body 104 on which a product No. and/or a secret No. are to be marked. This decreases the degree of freedom for marking.